The Proposal consists of three main components
- Removal of flow restrictions
- Bridge modifications
- Road raise/levee
Flow restrictions were identified as areas of high ground that could be adversely affecting the conveyance of water in the natural floodplain. Some examples include field roads that are at an elevation higher than the adjacent fields, roadways that lead to farmsteads that are no longer occupied, and ag levees built close to the outer bank meanders of the river. Initially, more than 70 potential flow restrictions were identified by members of the Border Township Associative Group (BTAG) and by an independent review of the floodplain.
Aerial imagery, topographic (LiDAR) data, and existing conditions flood inundation mapping were used as part of the review in order to identify potential flow restrictions. Intermediate study results indicated that some of the initially identified restrictions were not adversely impacting the floodplain elevations, and the 70+ initial restrictions were prioritized.
The proposed alternative includes the removal of approximately 40 restrictions. The proposed flow restriction removals were not optimized for maximum benefit during the study.
Intermediate study results indicated that removing flow restrictions alone provide some benefit to the area. However, increasing the capacity of existing bridges in combination with removing flow restrictions provides additional benefit. The bridges that are modified as part of this study include the NPR bridge and ND 54/MN 1 bridge over the Red River as well as the NPR bridge and ND 54 bridge over the Marais River. The modifications to the ND 54/MN 1 bridge over the Red River also includes excavation of material in the west channel overbank immediately downstream from the bridge.
Modifications were also made to the approaches to the ND 17/MN 317 bridge north of Oslo. The bridge approaches are proposed to be lowered for approximately 1 mile. The proposed bridge spans were maximized based on existing landscape features near the structures.
Road Raise and Levees South of Oslo
Intermediate study results indicated that removal of the flow restrictions and modifications to the bridges would result in a decrease of water surface elevation near the Oslo area. While the water surface elevations were reduced, there were only minor changes to the overall floodplain and impacts to the transportation infrastructure still existed. A road raise/levee component was analyzed south of ND 54 and Oslo to contain floodwaters near the river channels and to keep floodwaters away from I-29, ND 54, and MN 1. The road raise/levee was analyzed for a range of elevations in order to optimize the benefit while minimizing the adverse impacts.
North Dakota Side
The 16th St NE (Shane Road) road raise/levee would be constructed to the 5-year water surface elevation plus 0.1 feet (5-year + 0.1’). For events up through the 5-year elevation, the road raise/levee would not overtop. A secondary road raise/levee alignment would be constructed on the east side of I29 and a portion of ND54 would be raised to the 20-year water surface elevation plus 0.5 feet (20-year + 0.5’). For events up through the 20-year event, the secondary road raise/levee would not overtop. This would provide 20-year protection for I-29 and ND 54.
A road raise/levee alignment would extend south from the Oslo Levee and tie in to high ground on the north spoil bank of Judicial Ditch #1. The road raise/levee would be raised to the 20-year water surface elevation plus 0.5 feet (20-year + 0.5’). For events up through the 20-year event, the road raise/levee would not overtop. This would provide 20-year protection for MN 1.